Signal combining circuit



Feb. 2, 1960 R. T. BUESING 2,923,888

SIGNAL COMBINING CIRCUIT Filed Aug. 27, 1954 RICHARD T. BUESING,

H TORNEY.

United States Patent ice 2,923,888 SIGNAL COMBINING CIRCUIT Richard T. Buesing, Liverpool, N.Y., assignor to General Electric Company, a corporation of New York Application August 27, 1954, Serial No. 452,677

9 Claims. (Cl. 330124) The present invention relates in general to signal mixing circuits and has as a particular object thereof to provide a simple and improved circuit for mixing two signals in variable proportions. I

Heretofore, when it was necessary to mix in variable proportions two signals to obtain a combined output as, for example, to mix audio signals from a phonograph pickup and from a microphone to obtain a combined output, or to mix the outputs of two receivers, each of the signals was individually attenuated and thereafter was combined in a common impedance. Such an arrangement required two attenuators.

The present invention is directed to providing a circuit of this character in which a single potential dividing element is utilized as a mixing element and which is so arranged as to simultaneously vary in opposite senses the proportions of two signals appearing in the combined output of these two signals.

Accordingly, it is also an object of this invention to provide an improved circuit for combining a pair of signals in variable proportions by means of a single potential divider.

Briefly, in accordance with a specific embodiment of the invention, signal combining apparatus is provided comprising the combination of a low internal impedance source of a first signal, a high impedance source of a second signal, a potentiometer having a pair of fixed terminals and a tap variable in position between the fixed terminals, and means for applying the output of the high impedance source between the fixed terminals and for coupling the low impedance source directly across the variable tap and one of the fixed terminals. The characteristic of the output signal produced across the fixed terminals is such that the relative portion of one signal with respect to the other signal is variable in accordance with the position of the variable tap.

The features of this invention desired to be protected are pointed out in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description when taken in connection with the accompanying drawing wherein there is shown a schematic diagram of a circuit embodying this invention.

Referring now to the single figure of the drawing, there is shown a circuit embodying the present invention in which is provided a high impedance source 1, including an electron discharge device 2, connected between a pair of terminals 3 and 4 of, a potential divider 5 for supplying thereto a signal to be mixed. The terminals 3 and 4 are fixed terminals at respective ends of potential divider 5. A low impedance source 6, including an electron discharge device 7 is also provided having its output connected between terminals 8 and 4 of the potential divider 5, for supplying another signal between the terminals 4 and 8 of potential divider 5. The terminal 8 is a tap that is movable between the terminals 3 and 4 of the potential divider 5. The combined output is obtained patented Feb. 2, 1960 tional operating potential. Negative terminal 14 is con nected to ground. The grid 12 is connected through. grid leak resistance 16 to the cathode 11. The grid 12 is also connected through a coupling capacitor 17 to one of a pair of input terminals 18, the other of which, 19, is connected to ground. A terminal resistance 20 is connected in shunt with the input terminals 18 and 19. The anode 13 is connected through anode load resistance 21 to the positive terminal 22 of source 15. The anode 13 is also connected through a coupling capacitor '23 and a level controlling resistor 24 to terminal 3 of potential divider 5.

Electron discharge device 7 includes a cathode 25, a grid 26, and an anode 27. The cathode 25 is connected through cathode resistance 28 to ground. The cathode 25 is also connected through coupling capacitor 29 and level controlling resistor 30 to the terminal 8 of potential divider 5. The grid 26 is connected through grid leak resistance 31 to ground and also connected through coupling capacitor 32 to one input terminal 33 of a pair of input terminals, the other of which, input terminal 34, is connected to ground. The anode 27 is connected to positive terminal 22 of source 15. A terminal resistance 35 is connected between input terminals 33 and 34.

Electron discharge device 10 includes a cathode 36, a grid 37, and an anode 38. Cathode 36 is connected to ground, the grid 37 is connected through grid leak resistance 39 to ground and also through coupling capacitor 40 to terminal 3. The anode 38 is connected through anode load resistance 41 to the positive terminal 22 of source 15. The anode 38 is also connected through coupling capacitor 42 to one output terminal 43 of a pair of output terminals, the other of which, output terminal 44, is connected to ground.

One of a pair of signals desired to be combined is applied across input terminals 18 and 19 and the other is applied between terminals 33 and 34. The impedance of the amplifier 1 appearing between terminal 3 and ground is arranged to be substantially higher than the impedance of amplifier 6 appearing between terminal 8 and ground. Thus, when the terminal 8 is coincident with terminal 3, the output of amplifier 1 is substantially short circuited by the impedance of amplifier 6 and all of the output from amplifier 6 appears across the potential divider 5. When the terminal 8 coincides with the terminal 4, the output of the amplifier 6 is short circuited. When the terminal 8 is in a position intermediate with the terminals 3 and 4, the outputs from both amplifiers 1 and 6 appear across potential divider 5 in proportion to the position of terminal 8 with respect to terminals 3 and 4. Preferably, the impedance of potential divider 5 is made substantially larger than the impedance of the amplifier 6 appearing between terminal 8 and terminal 4. Also for a particular position of the terminal 8, the outputs of the amplifiers 1 and 6 may be arranged to obtain the proper portion of mixing for this position.- The output taken between terminals 3 and 4 is applied to an amplifier 9, and thence to output terminals 43 and 44.

While there has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects and it is, therefore, an aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim is new and desire to secure by Letters Patent of the United States is:

l. A signal mixing circuit comprising a first signal source, a first electron discharge device having a cathode, a grid and an anode, a ground connection, first coupling means coupling said grid to said first signal source, said cathode being coupled to said ground connection, said first electron'discharge device having a relatively high impedance between its anode and said ground connection, a second signal source, a second electron discharge device having a cathode, a grid and an anode, second coupling means coupling said grid of said second electron discharge device to said second signal source, a cathode resistor of relatively low resistance with respect to the impedance between the anode of said first electron discharge device and said ground connection, said cathode resistor being coupled between said cathode of said second electron discharge device and said ground connection, a potentiometer having first and second fixed terminals and a tap variable in position between said first and second fixed terminals, said second fixed terminal being connected to said ground connection, third coupling means coupling said anode of said first electron discharge device to said first fixed terminal, fourth coupling means coupling said cathode of said second elec tron discharge device to said tap, and output means coupled to said first fixed terminal of said potentiometer, the impedance path to said ground connection via said fourth coupling means being low relative to the impedance path to said ground connection via said first coupling means such that when said tap is in proximity to said first fixed terminal a signal from said first electron discharge device is substantially short circuited and such that when said tap in proximity to said second fixed terminal the signal from said second electron discharge device is substantially short circuited whereby the relative proportion of one signal with respect to the other of said signals appearing at said output means is variable in accordance with the position of said tap with respect to said first and second fixed terminals 2. A mixing circuit for mixing two signals comprising first and second signal control means each having a control element and a controlled element, the control element of said first signal control means being responsive to one signal and the control element of said second signal control means being responsive to the other signal, a reference potential source, said first signal control means having a relatively high impedance between its controlled element and said reference potential source,

an impedor having low impedance relative to the impedance between the controlled element of said first signal control means and said reference potential source, said impedor being coupled between said controlled element of said second signal control means and said reference potential source, a potentiometer having first and second terminals and a tap variable in position between said first and second terminals, said second terminal being coupled to said reference potential source, first coupling means coupling the controlled element of said first signal control means to said first terminal, second coupling means coupling the controlled element of said "second signal control means to said tap, output means, and third coupling means coupling said output means to said first terminal, the impedance path from said tap via said second coupling means to said reference potential source being low with respect to the impedance path from said first terminal via said first coupling means to said refer ence potential source such that when said tap is in proximity to said first terminal, the signal from said first signal control means substantially bypasses said potentiometer and such that when said tap is in proximity to said second terminal substantially all of the signal from said second signal control means is fed directly to said reference potential source whereby the relative portions of one signal with respect to the other of said signals appearing at said output means is variable'in accordance/with a d the position of said tap with respect to said first and second terminals.

3. A circuit comprising a first signal source having a first predetermined internal impedance, a second signal source having a second predetermined internal impedance, a potentiometer having a predetermined resistance, said potentiometer having first and second terminals and a tap variable in position between said first and second terminals, means for applying a signal from said first signal source across said first and second terminals, means or applying a signal from said second signal source directly across said tap and said second terminal, a source of reference potential connected to said second terminal, and output means responsive to said potentiometer, said first and second predetermined internal impedances and said predetermined resistance being such that a relatively low impedance is presented to said first signal source when said tap is in proximity to said first terminal thereby bypassing "substantially all of the signal from said first signal source around said potentiometer and to said source of reference potential and such that when said tap is in proximity to said second terminal substantially all of the signal from said second signal source is fed to said source of reference potential whereby the relative portions of the signals at said output means from said first and second signal sources is variable in accordance with the position of said tap with respect to said first and second terminals.

4. In combination, a low internal impedance source of a first signal, a high internal impedance source of a second signal, a potentiometer having a pair of fixed terminals and a tap variable in position between said fixed terminals, means for applying the output of said high impedance source between said fixed terminals, and means for coupling said low impedance source directly across said variable tap and one of said fixed terminals for producing an output signal across said fixed terminals having a characteristic such that the relative portion of one signal with respect to the other of said signals appearing in said output signal is variable in accordance with the position of said tap with respect to said fixed terminals.

5. In a circuit for combining two difierent kinds of signals, a low internal impedance source of a first kind of signals, a high internal impedance source of a second kind of signals, a potentiometer having a pair of fixed terminals and a tap variable in position between said fixed terminals, means for applying the output of said high impedance source between said fixed terminals, and means for coupling said low impedance source directly across said variable tap and one of said fixed terminals for producing an output signal across said fixed terminals having a characteristic such that when said low impedance source is in shunt with said high impedance source, said high impedance source is substantially short circuited, and the relative portion of one signal with respect to the other of said signals appearing in said output signal is variable in accordance with the position of said tap with respect to said fixed terminals.

6. In a-circuit for combining two different kinds of signals, a lowinternal impedance source of a first kind of signals, a highiinternal impedance source of a second kind of signals, a resistance divider havinga pair of fixed terminals and a tap variable in position between said fixed terminals, the internal impedance of said high impedance of said resistance divider being substantially greater than the internal impedance of said low impedance source,'means for applying the output of said high impedance source across said fixed terminals, and means for applying the output of said low impedance source directly across said variable tap and one of said fixed terminals for producing an output signal across saidfixed terminals having a characteristic such that the relative portion of one signal with respect to the other of said signalsappearing-insaidoutput'signal is variable in accordance with the position of said tap with respect to said fixed terminals.

7. In a circuit for combining two signals, a low internal impedance source for one of said signals, a high internal impedance source for the other of said signals, a potentiometer having a pair of fixed terminals and a tap variable in position between said fixed terminals, means for applying the output or" said high impedance source across said fixed terminals, and means for applying the output of said low impedance source directly across said tap and one of said fixed terminals for producing an output signal across said fixed terminals having a character istic such that the relative portion of one signal with respect to the other of said signals appearing in said output signal is variable in accordance With the position of said tap with respect to said fixed terminals.

8. Signal combining apparatus comprising first and second signal sources, said first and second signal sources each having first and second output terminals, signal divider means having first and second fixed terminals and a movable terminal operatively movable intermediate said first and second fixe'd terminals, means for directly coupling the first and second output terminals of said first signal source to the first and second fixed terminals of said signal divider means, means for directly coupling the first output terminal of said second signal source to the second fixed terminal of said signal divider means, and means for directly coupling the second output terminal of said second signal source to the movable terminal of said signal divider means so that said first and second signals apply, in parallel, signals to said signal divider means. I

9. The signal combining apparatus of claim 8 wherein said first signal source has a high internal impedance and said second signal source has a low internal impedancc.

References Cited in the file of this patent UNITED STATES PATENTS 2,282,319 Brown May 12, 1942 2,663,843 Wickerham et al. Dec. 22, 1953 2,692,358 Wild Oct. 19, 1954 2,705,794 Sunstein Apr. 5, 1955 FOREIGN PATENTS 399,550 Great Britain Oct. 9, 1933 594,684 Germany Mar. 21, 1934 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 923 888 February 2 1960 Richard T. uesing It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 3 line 32., after "tap" insert is column 4, line 66 after "pedance" insert source and the impedance Signed and sealed this 11th day of October 1960.

SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 923 888 February 2 1960 Richard T. Buesing It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 3 line 32 after "tap" insert is column 4, line 66 after 'pedance" insert source and the impedance Signed and sealed this 11th day of October 1960.

SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

